The operator of a vehicle, particularly a lift truck, is required to manipulate one or more hand control levers for hoisting a load and tilting the mast of the truck and is also required to steer the vehicle. Since the operator must also manipulate hand control levers to propel the vehicle in the forward and reverse directions, it is evident that some operations must be performed sequentially rather than simultaneously. Such operation increases loading time and reduces productivity.
An attempt at providing simultaneous control is disclosed in U.S. Pat. No. 2,968,967 granted on Jan. 24, 1961 to Cecil J. Ross Jr. in which a foot control lever controls the forward and reverse motion of the vehicle. By using a foot pedal to change directions, the hands are free for steering and manipulating the load. However, the pedal is always in one of the forward and reverse directions even when the foot is removed from the pedal. It is possible to depress both the forward and reverse switches simultaneously with the result that the operator does not know the direction in which the vehicle will travel.
It is desirable to have a directional control which returns to neutral when both the forward and reverse switches are activated at the same time. It is also desirable to have a single directional control which is useable with internal combustion engine vehicles and with electric vehicles.
Solenoids are typically used to shift valves and move levers to control vehicle direction. Where the lever moves in two directions, two solenoids are used, one to move the lever in each direction. Since solenoids remain energized for a period of time after the power source is removed, the solenoid must have time to deenergize before the second solenoid is energized so that the lever can move. It is desirable to have a control circuit which directs current through each solenoid in a selected direction and which delays operation of one solenoid until the other has deenergized.
In vehicles, such as lift trucks which have inductive motors, there are transient voltages of greater magnitude than the nominal rated voltages of the vehicle systems which are often great enough to damage the solenoids or other circuit components. It is desirable to provide transient and overcurrent protection for the solenoids and other circuit components.
Current internal combustion engine lift trucks use a stick selector for choosing the forward or reverse direction of travel while electric lift trucks use a dash mounted electrical switch. It is desirable to have a foot actuated directional control circuit which is useable with electric and internal combustion engine lift trucks.